In a paper mill a continuous strip of paper moving longitudinally at high speed must be transversely cut into individual sheets that must then be piled in individual stacks on pallets or the like. The stacking must be done without interrupting the flow of continuously arriving sheets, so that when a stack is complete it is necessary to get it out of the way and bring a new pallet into place while somehow catching and holding the sheets that arrive during the changeover.
Commonly owned U.S. Pat. No. 5,628,595 describes an apparatus having a downstream end spaced upstream in a horizontal transport direction from a stacking station for delivering the sheets continuously one after the other at a predetermined upper level in the direction to the station and a main platform vertically displaceable in the stacking station between an upper position below the upper level and a lower position. An auxiliary platform below the upper level is formed by a plurality of parallel rods horizontally displaceable in the direction between an extended position in the station above the main platform and a retracted position upstream of the main platform. A plurality of vertically extending separator elements having bent-over upper ends projecting downstream between the rods in the transport direction are displaceable between a separating position projecting into the station between the auxiliary platform and the upper level and engaged between trailing edges of sheets and a withdrawn position out of the station between the station and the conveyor downstream end. Each element has a vertical length greater than the vertical distance between the auxiliary platform and the upper level.
German patent 2,749,912 issued Nov. 8, 1971 to R. Schmitz shows an arrangement where the sheets are deposited on a platform that is lowered in a frame as the stack formed on the platform grows. The platform is suspended from cables and can, when fully loaded, weigh several tons. It is sometimes moved vertically as much as 3 m. Obviously if, for instance, one of the cables broke and the loaded platform dropped, it could do considerable damage to the apparatus. Accordingly this German patent proposes an antidrop mechanism that arrests the platform by jamming toothed guide wheels into a stationary rack. Such a system is effective but fairly complex.